Medical implants such as, for example, pacemakers and defibrillators often include an electrical connection to the inside of the patient's body. A connection of this type is generally used to measure electrical signals and/or stimulate cells of the body. This connection is usually an electrode lead of the type described above. Currently, electrical signals are transmitted between the implant and the electrode contacts (e.g., tip, rings, HV shock helixes, sensors, etc.) using materials having good electrical conductivity.
If a system comprised of an implant and an electrode is exposed to strong interference fields (e.g., EMI, MRI), unwanted consequences can occur, especially a heating-up of parts of the system or electrical malfunctions (i.e., resets). The heating can result in damage to bodily tissue or organs if the heated parts have direct contact with such tissue. This is the case with the electrode tip, in particular.
The unwanted malfunction is generally caused by the interaction of the field with the elongate lead structure of the electrode: The electrode functions as an antenna and receives energy from the surrounding fields. The antenna can dissipate this energy on the leads, which are used for therapeutic purposes, distally into the tissue via the electrode contacts (e.g., tip, ring, etc.), or proximally into the implant. Similar problems occur with other elongate conductive structures, the proximal end of which is not necessarily connected to an implant (i.e., catheters, temporary electrodes, etc.).
Shielded electrodes are known. The shielding of the electrode mainly counteracts electrical fields that are coupled in from the outside. In addition, these shieldings provide only a particular shielding strength and are stable over the long term. A compromise must therefore be found between increasing the diameter of the electrode—which would have a corresponding effect on the costs and handling of the electrode—and a diminished shielding effect. Due to the high requirements on biocompatibility and biostability, materials that have proven useful in terms of the shielding effect thereof, e.g., soft magnetic nickel-iron alloys, cannot be used.
To prevent interferences by magnetic alternating fields and, in particular, in magnetic resonance apparatuses (MRI), especially to limit the heating of the electrode tip in fields of this type, it was proposed in U.S. Publication No. 2008/0243218 to provide a protective conductor in an electrode lead that turns back on itself in the longitudinal direction. This “billabong” principle utilizes mutual inductances to diminish induced currents. In this case, however, the three-layered helical winding is likewise expected to increase the diameter of the electrode.
The present inventive disclosure is directed toward overcoming one or more of the above-identified problems.